The present invention relates generally to the tracking of mobile assets such as cargo containers, and in particular to techniques for reducing power consumption.
The management of mobile assets is a major concern in various transportation businesses such as the trucking, railroad, and rental car industries. As one example, in the trucking industry, an asset manager must keep track of the status and location of both the tractors and the trailers in a fleet. The asset manager should know whether each trailer asset is in service (i.e. being transported by a tractor or other means) or out of service (i.e. not being transported by a tractor). The asset manager should also have similar information with respect to whether each tractor asset is hauling a trailer, or not present hauling anything. It should also be possible to monitor progress of each tractor and trailer so that the asset manager may develop a plan for scheduling purposes.
Systems for tracking and monitoring mobile assets for fleet management are therefore generally known in the art. These systems typically include various electronic sensors connected to monitor the asset, and wireless communication systems, used to report the asset status.
The sensors are typically installed within the tractor or cargo trailers in such as way that they can automatically monitor the status of each asset. One common type of sensor is one that determines the location of a unit, such as a Global Positioning System (GPS) receiver. Other sensors provide status on proper operating conditions (such as temperature), detect misuse (such as by detecting an unscheduled “door open” event) and otherwise monitor the progress of each tractor and trailer for scheduling and security purposes.
In the typical arrangement, the electronics package within a cargo trailer, for example, can include various sensors for determining status, a GPS unit for determining a location, and a cellular radio modem for reporting data concerning current position and status to a central location. When the trailer is in a tethered mode (that is, when it is connected to a tractor), the vehicle's electrical system provides ample current for powering these electronics. When a trailer is disconnected from the tractor (that is, in an untethered mode), power consumption can become an issue. A trailer may remain untethered for many hours, or days (even weeks) in a storage yard. Since such electronics are expected to continue to operate, even in the absence of available external power from a tractor, the electronics must typically draw current from a local battery. However, in order to avoid running down that local battery, such units will enter a low power mode until such time as vehicle motion is indicated by a GPS, accelerometer, or other motion sensor, that provide confirmation that the trailer is actually moving.